中温沥青超声萃取物的热解特性与分子结构间关联性的FTIR解析

沥青分子结构和沥青热转化行为的调控是制备高品质沥青基炭材料的关键。为进一步明晰沥青热解行为与沥青分子结构间的关联性，选用8种有机溶剂对中温沥青（AGMP）在常温下进行超声萃取处理得到8 种萃取物。利用 PeakFit v4.12 软件对各种萃取物的红外光谱吸收峰700~900，1 000~1 800，2 800~3 000和3 000~3 100 cm-1四个区域进行了分峰拟合处理，从而获得了萃取物所含各种官能团的精细结构信息，并引入6种分子结构参数（I₁~I₆），表征萃取物分子结构与热解活化能的关系。傅里叶变换红外光谱(FTIR)谱图分析表明8种萃取物主要是以含氧、含氮等杂原子的脂肪烃侧链为主的缩合芳香环结构组成的复杂化合物。由于萃取剂结构差异，萃取物中的分子结构参数也略有差异。线性结构萃取剂所得萃取物链烃（I₅）含量较高，环结构萃取剂所得萃取物芳环（I₆）取代结构较多。利用热重分析法（TGA）在不同升温速率（3，6，10，15 K·min-1）下对8种萃取物的热失重行为进行了研究，在等转化率不考虑反应机理的情况下，依据Flynn-Wall-Ozawa法和Kissingr-Akahira-Sunose 法解析得出8 种萃取物的热解活化能（E_a）。结果表明8种萃取物热解活化能在78～116 kJ·mol-1之间，其值大小与官能团结构及含量密切相关。将红外光谱定量分析获得的萃取物红外结构参数与热解活化能进行关联，通过详细分析探讨不同萃取物结构参数与热解活化能的一元线性回归E_a=f(I_i)的分析结果发现，芳香性指数（I₃）和支链化程度（I₅）是决定萃取物热解活化能大小的主要指标，热解活化能与各单一指标（I_i）拟合结果的正负相关性，表示这一结构从体系中被热解破坏的难易程度。综合考虑各红外结构参数的共同作用，AGMP萃取物热解活化能与红外光谱结构指标之间的拟合关系模型为E_a=-4 294.53I₁+73 812.16I₂+207 673.32I₃-20 324.20I₄-168.56I₅+857.86I₆。结合红外分析得到的这一结果，揭示了更多关于煤沥青的热解特性和动力学的细节信息，有助于理解煤沥青的热解过程和热转化行为。

FTIR Analysis of the Correlation Between the Pyrolysis Characteristics and Molecular Structure of Ultrasonic Extraction Derived From Mid-Temperature Pitch

The regulation of molecular structure and thermal conversion behavior of coal tar pitch is the key to preparing high-quality coal tar pitch-based carbon materials. In order to further clarify the relationship between pyrolysis behavior and molecular structure of coal tar pitch, 8 kinds of extracts derived from Medium temperature pitch (AGMP) were extracted by ultrasonic extraction with 8 kinds of organic solvents at room temperature in this paper. The PeakFit v4.12 software was used to perform peak fitting the infrared spectra of the extracts in four regions of 700~900, 1 000~1 800, 2 800~3 000 and 3 000~3 100 cm-1 to achieve the fine structure information about various functional groups. In addition, six molecular structure parameters (I₁-I₆) were introduced to characterize the relationship between molecular structure and pyrolysis activation energy of the extracts. FTIR spectra analysis shows that the 8 extracts are complex compounds composed of condensed aromatic ring structures mainly comprised of aliphatic hydrocarbon side chains containing oxygen and nitrogen and other heteroatoms. Moreover, due to the difference in the extractant’s structure, the extract’s molecular structure parameters are also slightly different. The extract obtained from the linear structure extractant has a higher content of chain hydrocarbons (I₅), and the extract obtained from the ring structure extractant has more aromatic rings substituted structures (I₆). Thermogravimetric analysis (TGA) was used to study the thermal weight loss behavior of 8 extracts at different heating rates (3, 6, 10, 15 K·min-1). Under the condition of equal conversion rate without considering the reaction mechanism, the pyrolytic activation energy (E_a) were calculated and analyzed using the Flynn-Wall-Ozawa method and Kissingr-Akahira-Sunose method. The results indicated that the eight extracts’ pyrolytic activation energies ranged from 78 to 116 kJ·mol-1, which are closely related to the structure and content of functional groups. The structural parameters of the extracts obtained by IR quantitative are correlated with the pyrolysis activation energy. The fitting results of the one-element linear equation E_a=f(I_i) between the structural parameters of the extracts and the pyrolysis activation energy found that the aromaticity index (I₃) and the degree of branching (I₅) are the two main indicators that determine the pyrolysis activation energy of the extracts. The fitting results of positive and negative correlation between the pyrolysis activation energy with every single index (I_i) indicate the difficulty of the structure being destroyed by pyrolysis. Considering the interaction of various infrared structural parameters, the fitting relationship model between the E_a of AGMP extracts and the infrared spectral structure indexes was shown as followed: E_a=-4 294.53I₁+73 812.16I₂+207 673.32I₃-20 324.20I₄-168.56I₅+857.86I₆. The results, which combined analysis of FTIR spectra, reveal more details about thermal characterization and kinetic characterization and they can be expected to lead to a well-understood coal tar pitch’s pyrolysis.